[SDBM-1807] Do not submit plan events when plan definition has been evicted from cache

[natashadada]

There are cases where we are not able get a plan from the cache (ex. sqlserver evicted the relevant plan to free up memory). When this happens, we still submit a plan event with a plan signature but no plan definition. When querying for plans this is a bit weird since we say we've collected a plan because we see a plan event with a plan signature but we don't have the actual plan to show the user.

I see a few options here:

1. We can not submit plan events if we don't have the plan definition. This makes the most sense to me right now but would appreciate other perspectives/things I may be missing
2. We could submit the plan with a collection_error that says the plan is null because it was not found
3. We could leave plan collection as is and change the way we query for plans on the front end (only query for plan events with a plan definition)

This PR is for option 1. If there is a collection errors, then we still submit the plan but if there's not collection error and no plan definition, we skip the plan event. We have a log line when we fail to load plan, so users can still see when this happens and we can see it in debug flares.

If a plan is encrypted, we don't get a plan definition. In this case, I am adding a collection error. I will update the front end to have support for this error in https://github.com/DataDog/web-ui/pull/212997.

Support ticket: https://datadoghq.atlassian.net/browse/SDBM-1807

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.38%. Comparing base (077bcac) to head (42def46).
Report is 13 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
confluent_platform	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?
sqlserver	91.27% <100.00%> (+5.30%)	⬆️
tomcat	?
weblogic	?

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